1. Field of the Invention
This invention relates to miniature lasers and other optical devices that use optical contacting methods to affix polished components to one another.
2. Description of the Prior Art
In many optical applications, it is desirable to rigidly join two polished components into a composite optical assembly. Compound lenses, for example, may consist of two or more elements with different indices of refraction and/or dispersion. In certain cases, adjoining surfaces are polished to the same radius of curvature and joined to each other to form a single unit. Techniques for joining the two materials include a variety of optical cements and epoxies that may be cured with the help of UV radiation or heat and, in some cases, optical contacting.
While adhesives are commonly used for low power applications, they often degrade in the presence of high-powered laser radiation. Optical contacting techniques are free from this problem since the surfaces to be joined are placed in direct contact with one another. These techniques have most commonly been used in the optical shop to rigidly affix two components (typically of the same material) for polishing or other operations. Finished optical components, such as air-gapped etalons and zero-order waveplates, have also been assembled via optical contacting and, in the absence of particulate contamination or temperature gradients, form robust mechanical assemblies.
Optical contacting has also been used for the assembly of miniature laser devices. U.S. Pat. No. 5,651,023 describes an intracavity-frequency doubled laser microlaser device consisting of at least three planar optical components. According to this patent, assembly via optical contacting is a preferred embodiment that leads to low cost, mechanically rugged devices. In addition, advantageous etalon effects can be achieved by using components with dissimilar indices of refraction that produce advantageous frequency selective etalon effects when the optical path length of the individual components is carefully controlled. U.S. Pat. No. 5,796,766 discloses several microlaser devices in which one of the optically contacted intracavity components is used to mount and heat sink the assembly. U.S. Pat. No. 5,838,713 describes a tunable, blue, intracavity-doubled microlaser in which one surface of the nonlinear contacted mounting plate crystal is optically contacted to the gain medium for compactness and ease of assembly.
In these cases where the optically contacted surfaces are placed inside a laser resonator, it is desirable to reduce the optical losses associated with the interface to a level that makes them insignificant with respect to other sources of intracavity loss (coatings, bulk crystal loss, etc.). In intracavity-frequency doubled lasers, for example, the nonlinear conversion efficiency increases superlinearly with intracavity power. Since this power increases rapidly with decreasing loss, it is desirable to reduce the intracavity loss to the lowest possible value. Possible sources of losses at the optically contacted intracavity interface between two materials include scattering, debonding due to differential thermal expansion and inhomogeneities due to localized variations in the optical properties of the bonded surfaces.
Therefore, it would be an advantage to provide an optical contacting method that reduces the optical losses at the interface between the component pieces of an optically contacted microlaser assembly. Ideally, such a method could be used with commonly-employed gain and nonlinear optical materials including neodymium-doped YAG and neodymium-doped yttrium vanadate, chromium-doped lithium strontium aluminum fluoride, potassium titanyl phosphate, beta barium borate and lithium triborate. It would be additionally advantageous if the improved optical contacting technique offered measurable improvements in the losses and/or homogeneity of optically contacted surfaces designed for use outside of a laser resonator.